Plastics/metal composite components which are produced by the injection molding of thermoplastic plastics material around functional elements have recently become widely used in the automotive and electrical industry,. Components for electrical applications, in which contact ducts through a housing wall are required, e.g., automotive fuse boxes or sensor housings, may be produced by the process of direct injection molding around elements. In such processes, a thermoplastic plastics material, e.g., a molding composition containing polyamide (PA) or polybutylene terephthalate (PBT) or PBT blend, is injection molded around the contact ducts, which are fixed in a cavity of an injection-molding tool. The contact ducts may be, for example, stamped metal sheets, which may be fabricated from copper or alloys containing copper. By means of the process of injection molding around elements it is also possible to integrate printed circuit boards, strip conductors or the like into the final molded plastics housingsmold.
The Applicants of the present invention realized that the process has the disadvantage, however, that only minimal adhesion is in most cases achieved between the metal components and the plastics components, so that the resulting composite is frequently not tight to media. Leakages therefore occur, which typically can only be eliminated by complex measures, e.g., by sealing with silicone or by treating the surface of the metal beforehand with an adhesion promoter (e.g., polyurethane dispersions, ethylene-vinyl acetate copolymer).
Adhesion of the plastics material to the metal may be also improved by preheating the metal. In order to achieve very good adhesion, however, it is necessary to bring the metal parts to a temperature in the region of the melting temperature of the thermoplastic material. Such a practice typically is not practical, especially in the case of thin-walled metal components, e.g., stamped metal sheets used for electrical applications. The temperature of corresponding injection-molding tools, at 60 to 90° C., is so low that even thoroughly preheated thin-walled metal parts inserted in the injection-molding tool cool to an unacceptably low temperature before the molten plastics material is injection molded around them.